A drill hammer with detachable tool holding fixture possessing the above-described characteristics was described in EP 0 448 801 A1. The tool holding fixture is mounted on a spindle sleeve by means of balls, which are held in recesses of the tool holding fixture and in holes of the spindle sleeve by a rotatable, but axially nondisplaceable ring, which is provided with openings. The ring is located within a clamping collar. To remove the tool holding fixture, the ring can be held through the clamping collar. After a rotation, the balls must then be removed from the outside. For example, a bar magnet is necessary for this. This is complicated, and the balls may be lost.
A tool changing device for a drill hammer is described in DE 34 09 494 C2. Standard drills or hammer drills can be inserted into the tool holding fixture. The tool holding fixture as a whole is an assembly unit. It is expensive because of the various possibilities integrated in it. Its true running property seems to need to be improved.
The tool holding fixture according to DE 34 09 494 C2 cannot be removed from the drill hammer for changing the tools. If a hammer drill is to be replaced with a standard drill, the latter is to be fixed by means of a drill chuck key. This prolongs the time needed for the tool change.
A device similar to that described in DE 34 09 494 C2 is described in DE 34 05 102 C2.
A drill hammer, in the guide tube of which various tool holding fixtures can be inserted, is described in DE 38 28 309 A1. However, the two tool holding fixtures described are to be fixed on the guide tube with different means.
In one case, the tool holding fixture, designed as a jaw chuck, is held by means of locking balls, which are located in holes of the tool holding fixture and in perforations of the guide tube. The balls are blocked radially by a ring, which is axially displaceable. The ring is covered from the outside and poorly accessible. The removal of the tool holding fixture is not described. At any rate, it is not simple, and the balls may fall out after removal.
In the second case, the tool holding fixture with radial projections and with a hidden pin is connected to the guide tube. The pin must be pulled for removal. The pin may be lost after it has been pulled.
DE 34 43 186 A1 discloses a drill hammer, in which an externally exposed outer sleeve is mounted axially displaceably, as a result of which the overall length of the drill hammer is increased by the path of displacement of this outer sleeve.
A hand-operated machine tool, in which tool change is possible through a rotatable outer sleeve, is described in DE 36 36 027 A1.